Alumina ceramic powder and preparation process thereof

Abstract

The present invention relates to the technical field of alumina ceramics, and discloses an alumina ceramic powder and a preparation process thereof. The present invention uses titanium dioxide micropowder as a sintering aid, phthalic acid modified starch as a pore former and dispersant, and α-Al2O3 micropowder through ball milling, aging, molding, sintering and other processes to prepare porous alumina ceramics. Phthalic acid modified starch can be a dispersant to improve the dispersibility of α-Al2O3 micropowder, reduce its agglomeration, improve the uniformity of alumina ceramics, and improve the flexural strength. Modified starch can be used as a pore former, pyrolyzes during high-temperature sintering, and leaves a rich and uniform pore structure in the alumina ceramic. The obtained alumina ceramic has a higher porosity and can maintain good flexural strength.

Description

Technical Field

[0001] The invention relates to the technical field of alumina ceramics, in particular to an alumina ceramic powder and a preparation process thereof. Background Art

[0002] Porous alumina ceramic materials have rich pore structures and exhibit properties such as high specific surface area, low thermal conductivity, and high seismic resistance. They can be made into sound-absorbing and shock-absorbing materials, filter materials, thermal insulation materials, chemical sensors and other materials. They are widely used in environmental protection, metallurgy, electrochemistry, petrochemicals and other fields.

[0003] Usually, porous alumina ceramic materials are made of Al2O3 micropowder as raw material, and are blended and sintered with binders, dispersants, pore formers, sintering aids, etc. Improving the porosity, strength and other properties of alumina ceramic materials is the focus of research, but when the porosity of alumina ceramics is large, its mechanical properties will be greatly affected. The patent with announcement number CN114933486B discloses a method for preparing porous ceramic blocks based on 3D printing of water-based slurry, using alumina powder, starch, binder, photoinitiator, dispersant, etc. as raw materials, and the prepared porous alumina ceramic blocks have the characteristics of high strength, high hardness, high wear resistance, etc. Compared with the invention, this aspect uses phthalic acid-modified starch as a dispersant and pore former, and the obtained porous alumina ceramics have good mechanical strength while maintaining high porosity. Summary of the invention

[0004] The invention solves the problems of poor dispersibility and poor mechanical properties of porous alumina ceramics.

[0005] The technical solution provided by the present invention is: a preparation process of alumina ceramic powder:

[0006] (1) Add pyridine and starch to a flask, heat to 100-110°C, stir for 1-2 hours, then cool in an ice-water bath, add trimellitic anhydride chloride, heat to 60-70°C, stir for 4-8 hours, remove pyridine by vacuum distillation, wash with dichloromethane, add the product to water, heat to 40-45°C, stir for 12-18 hours, and place the solution in a freeze dryer for freeze drying to remove water to obtain phthalic acid modified starch. The reaction formula is:

[0007] .

[0008] (2) Add water and 3-8 parts by weight of phthalic acid-modified starch to a ball mill, stir to dissolve, then add 100 parts by weight of α-Al2O3 powder and 1.4-2.8 parts by weight of titanium dioxide powder, and perform ball milling. Pour the obtained ball milling liquid into a sealed bag, and place it in an insulated box at 20-25°C for aging for 12-18 hours; then heat it in an oven at 90-100°C and dry it for 2-4 hours to obtain alumina ceramic powder.

[0009] Preferably, the mass of pyridine and trimellitic anhydride chloride is 1000-1500% and 200-500% of the mass of starch respectively.

[0010] Preferably, the rotation speed during ball milling is 200-300 r / min and the time is 10-25 min.

[0011] Preferably, the alumina ceramic powder is placed in a mold, and in a molding machine, the pressure is 20-30 MPa, and the molding is performed for 3-5 minutes to form a green body; finally, the green body is sintered to obtain a porous alumina ceramic.

[0012] Preferably, sintering is carried out in a muffle furnace in an air atmosphere at a heating rate of 2-3°C / min, first heating to 350-400°C and keeping warm for 30-40min; then heating to 600-700°C and keeping warm for 40-60min; then heating to 900-1000°C and keeping warm for 1-1.5h; finally heating to 1200-1250°C and keeping warm for 1.5-2h.

[0013] The technical effect of the present invention is as follows: the present invention utilizes starch and trimellitic anhydride acyl chloride to carry out acyl chloride esterification reaction and anhydride hydrolysis to obtain phthalic acid modified starch, which is used as a pore-forming agent and dispersant, and titanium dioxide micropowder is used as a sintering aid, and α-Al2O3 micropowder is subjected to ball milling and aging to obtain alumina ceramic powder, and then subjected to molding, sintering and other processes to prepare porous alumina ceramics. Phthalic acid modified starch contains phthalic acid structure, and interacts with the surface of α-Al2O3 micropowder by coordination and the like, so that the modified starch is used as a dispersant to improve the dispersibility of α-Al2O3 micropowder, reduce its agglomeration, improve the uniformity of alumina ceramics, and increase the bending strength.

[0014] The modified starch of the present invention can be used as a pore-forming agent, and is pyrolyzed during high-temperature sintering, leaving a rich and uniform pore structure in the alumina ceramic. The obtained alumina ceramic has a high porosity and can maintain good bending strength. DETAILED DESCRIPTION

[0015] The technical scheme in the embodiments of the present invention will be described clearly and completely below in conjunction with the embodiments of the present invention. The raw materials in the embodiments and comparative examples of the present application are all commercially available unless otherwise specified.

[0016] The average particle size of the α-Al2O3 powder of the present invention is 5.6 μm, and the average particle size of the titanium dioxide powder is 200 nm. Starch and carboxymethyl starch, Langfang Jiangzhou Technology Co., Ltd.

[0017] Example 1

[0018] (1) Add 25 g of pyridine and 2 g of starch to a flask, heat to 100°C, stir for 2 h, then cool in an ice-water bath, add 6 g of trimellitic anhydride chloride, heat to 60°C, stir and react for 4 h, remove pyridine by vacuum distillation, wash with dichloromethane, add the product to water, heat to 45°C, stir and react for 12 h, place the solution in a freeze dryer to freeze-dry and remove water to obtain phthalic acid modified starch.

[0019] (2) Add 60 mL of water and 3 g of phthalic acid-modified starch to a ball mill, stir to dissolve, then add 100 g of α-Al2O3 powder and 2 g of titanium dioxide powder, and ball mill for 10 min at a speed of 300 r / min; pour the ball milling liquid into a sealed bag and let it stand in an insulated box at 25°C for 12 h; then heat it in an oven at 90°C and dry it for 3 h to obtain alumina ceramic powder.

[0020] (3) The alumina ceramic powder is placed in a mold and pressed in a molding machine at a pressure of 25 MPa for 5 minutes to form a green body; finally, in a muffle furnace, in an air atmosphere, the temperature is first increased to 350°C at a heating rate of 2°C / min and kept warm for 40 minutes; then increased to 650°C and kept warm for 60 minutes; then increased to 900°C and kept warm for 1.5 hours; finally, the temperature is increased to 1250°C and kept warm for 1.5 hours to obtain a porous alumina ceramic.

[0021] Example 2

[0022] (1) Add 20 g of pyridine and 2 g of starch to a flask, heat to 100°C, stir for 2 h, then cool in an ice-water bath, add 4 g of trimellitic anhydride chloride, heat to 65°C, stir and react for 8 h, remove pyridine by vacuum distillation, wash with dichloromethane, add the product to water, heat to 40°C, stir and react for 18 h, place the solution in a freeze dryer to freeze-dry and remove water to obtain phthalic acid modified starch.

[0023] (2) Add 100 mL of water and 5 g of phthalic acid-modified starch to a ball mill, stir to dissolve, then add 100 g of α-Al2O3 powder and 2.8 g of titanium dioxide powder, and ball mill for 25 min at a speed of 200 r / min; pour the ball milling liquid into a sealed bag and place it in an insulated box at 20°C for 18 h; then heat it in an oven at 100°C and dry it for 2 h to obtain alumina ceramic powder.

[0024] (3) The alumina ceramic powder is placed in a mold and pressed in a molding machine at a pressure of 20 MPa for 5 minutes to form a green body; finally, in a muffle furnace, the temperature is raised to 400°C at a heating rate of 2°C / min in an air atmosphere and kept at that temperature for 30 minutes; then the temperature is raised to 600°C and kept at that temperature for 60 minutes; then the temperature is raised to 1000°C and kept at that temperature for 1 hour; finally, the temperature is raised to 1200°C and kept at that temperature for 2 hours to obtain a porous alumina ceramic.

[0025] Example 3

[0026] (1) Add 30 g of pyridine and 2 g of starch to a flask, heat to 110°C, stir for 1 hour, and then cool in an ice-water bath. Add 10 g of trimellitic anhydride chloride, heat to 70°C, stir and react for 5 hours, remove pyridine by vacuum distillation, wash with dichloromethane, add the product to water, heat to 45°C, stir and react for 12 hours, and place the solution in a freeze dryer to freeze-dry and remove water to obtain phthalic acid modified starch.

[0027] (2) Add 100 mL of water and 6 g of phthalic acid-modified starch to a ball mill, stir to dissolve, then add 100 g of α-Al2O3 powder and 1.4 g of titanium dioxide powder, and ball mill for 20 min at a speed of 300 r / min; pour the ball milling liquid into a sealed bag, and place it in an insulated box at 25°C for 12 h; then heat it in an oven at 90°C and dry it for 4 h to obtain alumina ceramic powder.

[0028] (3) The alumina ceramic powder is placed in a mold and pressed in a molding machine at a pressure of 30 MPa for 4 minutes to form a green body; finally, in a muffle furnace, the temperature is increased to 350°C at a heating rate of 3°C / min in an air atmosphere and kept at that temperature for 40 minutes; then the temperature is increased to 700°C and kept at that temperature for 40 minutes; then the temperature is increased to 1000°C and kept at that temperature for 1 hour; finally, the temperature is increased to 1250°C and kept at that temperature for 1.5 hours to obtain a porous alumina ceramic.

[0029] Example 4

[0030] (1) Add 25 g of pyridine and 2 g of starch to a flask, heat to 100°C, stir for 2 h, then cool in an ice-water bath, add 8 g of trimellitic anhydride chloride, heat to 70°C, stir for 8 h, remove pyridine by vacuum distillation, wash with dichloromethane, add the product to water, heat to 40°C, stir for 18 h, and place the solution in a freeze dryer to freeze-dry and remove water to obtain phthalic acid modified starch.

[0031] (2) Add 100 mL of water and 8 g of phthalic acid-modified starch to a ball mill, stir to dissolve, then add 100 g of α-Al2O3 powder and 2 g of titanium dioxide powder, and ball mill for 20 min at a speed of 300 r / min; pour the ball milling liquid into a sealed bag and place it in an insulated box at 25°C for 12 h; then heat it in an oven at 100°C and dry it for 2 h to obtain alumina ceramic powder.

[0032] (3) The alumina ceramic powder is placed in a mold and pressed in a molding machine at a pressure of 30 MPa for 3 minutes to form a green body; finally, in a muffle furnace, in an air atmosphere, the temperature is raised to 350°C at a heating rate of 2°C / min and kept at this temperature for 40 minutes; then the temperature is raised to 700°C and kept at this temperature for 60 minutes; then the temperature is raised to 900°C and kept at this temperature for 1.5 hours; finally, the temperature is raised to 1250°C and kept at this temperature for 2 hours to obtain a porous alumina ceramic.

[0033] Comparative Example 1

[0034] (1) Add 60 mL of water and 3 g of starch to a ball mill, stir to dissolve, then add 100 g of α-Al2O3 powder and 2 g of titanium dioxide powder, and ball mill for 10 min at a speed of 300 r / min; pour the ball milling liquid into a sealed bag and place it in an insulated box at 25°C for 12 h; then heat it in an oven at 90°C and dry it for 3 h to obtain alumina ceramic powder.

[0035] (2) The alumina ceramic powder is placed in a mold and pressed in a molding machine at a pressure of 25 MPa for 5 minutes to form a green body; finally, in a muffle furnace, the temperature is raised to 350°C at a heating rate of 2°C / min in an air atmosphere and kept at that temperature for 40 minutes; then the temperature is raised to 650°C and kept at that temperature for 60 minutes; then the temperature is raised to 900°C and kept at that temperature for 1.5 hours; finally, the temperature is raised to 1250°C and kept at that temperature for 1.5 hours to obtain a porous alumina ceramic.

[0036] Comparative Example 2

[0037] (1) Add 60 mL of water and 3 g of carboxymethyl starch to a ball mill, stir to dissolve, then add 100 g of α-Al2O3 powder and 2 g of titanium dioxide powder, and ball mill for 10 min at a speed of 300 r / min; pour the ball milling liquid into a sealed bag and place it in an insulated box at 25°C for 12 h; then heat it in an oven at 90°C and dry it for 3 h to obtain alumina ceramic powder.

[0038] (2) The alumina ceramic powder is placed in a mold and pressed in a molding machine at a pressure of 25 MPa for 5 minutes to form a green body; finally, in a muffle furnace, the temperature is raised to 350°C at a heating rate of 2°C / min in an air atmosphere and kept at that temperature for 40 minutes; then the temperature is raised to 650°C and kept at that temperature for 60 minutes; then the temperature is raised to 900°C and kept at that temperature for 1.5 hours; finally, the temperature is raised to 1250°C and kept at that temperature for 1.5 hours to obtain a porous alumina ceramic.

[0039] The three-point bending method was used to test the flexural strength of alumina ceramic samples. The sample size was 40 mm × 4 mm × 3 mm and the loading rate was 0.5 mm / min.

[0040] The porosity of alumina ceramics was tested according to the method of GB / T 1966-1996.

[0041] Table 1 Alumina ceramic performance test

[0042]

[0043] As can be seen from Table 1, Examples 1-4 use titanium dioxide powder as a sintering aid and phthalic acid modified starch as a pore former and dispersant, and the obtained porous alumina ceramics have high flexural strength while maintaining high porosity. This is because the phthalic acid modified starch contains a phthalic acid structure, which interacts with the surface of the α-Al2O3 powder by coordination, so that the modified starch acts as a dispersant, improves the dispersibility of the α-Al2O3 powder, reduces its agglomeration, improves the uniformity of the alumina ceramics, and increases the flexural strength. At the same time, the starch can be used as a pore former, and pyrolysis occurs during high-temperature sintering, leaving a rich and uniform pore structure in the alumina ceramics. The obtained alumina ceramics have a high porosity and can maintain good flexural strength.

[0044] Compared with Example 1, Comparative Example 1 adds starch, which does not contain a carboxyl structure and is difficult to interact with the surface of the α-Al2O3 micropowder, and cannot play the role of a dispersant. The dispersibility of the α-Al2O3 micropowder is poor and it is easy to agglomerate. The porosity of the alumina ceramic after sintering is low, and the flexural strength and mechanical properties are poor.

[0045] Compared with Example 1, Comparative Example 2 uses common carboxymethyl starch as a pore-forming agent and dispersant, and the porosity and flexural strength of the obtained alumina ceramic are also higher, but the flexural strength is lower than that of Example 1. This is mainly because the carboxyl content of carboxymethyl starch is less than that of the modified starch containing a phthalic acid structure in Example 1, resulting in a lower interaction between the carboxymethyl starch and the surface of the α-Al2O3 micropowder, and a weaker dispersion effect than that in Example 1, resulting in the flexural strength of the porous alumina ceramic after sintering being lower than that of Example 1.

[0046] This specific embodiment is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, a person skilled in the art may make non-creative modifications to the present embodiment as needed, and such modifications shall be protected by the patent law as long as they are within the scope of protection claimed in the present application.

Claims

1. A process for preparing alumina ceramic powder, characterized in that: The preparation process is: (1) Add pyridine and starch to a flask, heat to 100-110°C, stir for 1-2 hours, then cool in an ice water bath, add trimellitic anhydride chloride, heat to 60-70°C, stir for 4-8 hours, remove pyridine by vacuum distillation, add the washed product to water, heat to 40-45°C, stir for 12-18 hours, and freeze-dry to obtain phthalic acid modified starch; (2) Add water, 3-8 parts by weight of phthalic acid-modified starch to a ball mill, stir to dissolve, add 100 parts by weight of α-Al2O3 powder, 1.4-2.8 parts by weight of titanium dioxide powder, and ball mill. Pour the obtained ball milling liquid into a sealed bag for aging, and then heat and dry to obtain an alumina ceramic powder; The masses of the pyridine and trimellitic anhydride chloride are 1000-1500% and 200-500% of the mass of the starch respectively.

2. The process for preparing alumina ceramic powder according to claim 1, characterized in that: The rotation speed during the ball milling is 200-300 r / min, and the time is 10-25 min.

3. The process for preparing alumina ceramic powder according to claim 1, characterized in that: The aging treatment is carried out in an incubator at 20-25°C for 12-18 hours.

4. The process for preparing alumina ceramic powder according to claim 1, characterized in that: The heating and drying is carried out in an oven at 90-100° C. for 2-4 hours.

5. An alumina ceramic powder obtained by the preparation process according to any one of claims 1 to 4.

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